Usually, in order to manufacture a highly integrated semiconductor element, a following series of steps are generally performed: a conductive thin film such as a metal film as a conducting wiring material and an interlayer insulating film intended for insulation between the conductive thin films are formed on an element such as a silicon wafer, then a photoresist is uniformly applied onto the surface thereof to provide a photosensitive layer, which is selectively exposed, and developed to produce an desired resist pattern. Next, this resist pattern is used as a mask to perform a dry etching treatment on the interlayer insulating film to form a desired pattern on the thin film. Then, residues resulting from the resist patterning and the dry etching treatment (hereinafter, referred to as “dry etch residues”) and the like are completely removed by an ashing method that uses an oxygen plasma or a cleaning method that uses a cleaning liquid.
Recently, along with the progress of miniaturization of the design rules, signal transmission delay is becoming to govern the limit of high-speed processing. Therefore, the conducting wiring material is shifting from aluminum to copper that has lower electric resistance, and the interlayer insulating film is shifting from a silicon oxide film to a low-dielectric-constant film (a film with a dielectric constant smaller than 3; hereinafter, referred to as a “Low-k film”). As miniaturization of wiring progresses, however, increase in the density of current running through the wiring tends to cause electromigration of copper. Accordingly, techniques that use cobalt as a highly reliable wiring material as a replacement of copper have been proposed. In addition, introduction of a cobalt alloy as a cap metal for copper has been reported to suppress electromigration of copper. Moreover, when a resist is applied with a film thickness of 1 μm to a wiring pattern of less than 0.2 μm, the aspect ratio of the wiring pattern (a ratio obtained by dividing the film thickness of the resist by the line width of the resist) becomes too large, which causes problems such as breakdown of the wiring pattern. In order to solve such problems, a hardmask technique is often employed in which a titanium (Ti)- or a silicon (Si)-based film (hereinafter, referred to as a “hardmask”) is inserted between a film that is to be actually fabricated with a pattern and a resist film, such that the resist pattern is once transferred onto the hardmask by dry etching, and then this hardmask is used as an etch mask to transfer the pattern onto the film that is to be actually fabricated by dry etching. This method allows the gas for etching the hardmask to be exchanged with the gas for etching the film that is to be actually fabricated. Since the gas can be selected such that selectivity of the resist increases when the hardmask is etched while selectivity of the hardmask increases when the film to be actually fabricated is etched, it is advantageous in that a pattern can be formed with a thin resist. Furthermore, as a contact plug for connecting with the substrate, a contact plug made of tungsten (hereinafter, referred to as a “tungsten plug”) is used.
In a case where the dry etch residues are removed with an oxygen plasma, a Low-k film is exposed to an oxygen plasma and the like and damaged, causing a problem of significant deterioration of the electrical characteristics. Therefore, in order to manufacture a semiconductor element that uses a Low-k film, there is a need for a method of removing dry etch residues to an extent comparable to the oxygen plasma process, while suppressing damage on a Low-k film, cobalt, a barrier metal and a barrier insulating film. In some cases, there is also a need for suppressing the damage on tungsten so that it can further be used on a layer where a contact plug is exposed. Moreover, in a case where a hardmask is used, damage on the hardmask should also be suppressed.
Patent Document 1 proposes a wiring formation method that uses a cleaning liquid containing an inorganic base, a quaternary ammonium hydroxide, an organic solvent, a corrosion preventing agent and water. This cleaning liquid, however, is incapable of sufficiently removing the dry etch residues (see Comparative Example 5 described later).
Patent Document 2 proposes a wiring formation method that uses a cleaning liquid containing KOH, a quaternary ammonium hydroxide, an organic solvent, pyrazole and water. This cleaning liquid, however, is incapable of sufficiently removing the dry etch residues (see Comparative Example 6 described later).
Patent Document 3 proposes a method for preventing cobalt corrosion by using benzotriazole and the like. This method, however, is incapable of sufficiently removing the dry etch residues (see Comparative Example 7 described later).
Patent Document 4 proposes a method for preventing cobalt corrosion by employing a combination of 5-amino-1H-tetrazole and 1-hydroxybenzotriazole. This method, however, is incapable of sufficiently removing the dry etch residues (see Comparative Example 8 described later).
Patent Document 5 proposes a wiring formation method that uses a cleaning liquid containing an oxidant agent, a quaternary ammonium hydroxide, alkanolamine, an alkali metal hydroxide and water. Although this cleaning liquid is capable of removing the dry etch residues, it is incapable of suppressing the damages on the tungsten, the cobalt, the Low-k film and the hardmask, and thus cannot be used for the intended purpose (see Comparative Example 9 described later).
Patent Document 6 proposes a wiring formation method that uses a cleaning liquid containing an oxidant agent, amine, a quaternary ammonium hydroxide, an alkali metal hydroxide, an organic solvent and water. This cleaning liquid, however, is incapable of sufficiently suppressing the damages on the tungsten and the hardmask, and thus cannot be used for the intended purpose (see Comparative Example 10 described later).
Patent Document 7 proposes a method for preventing cobalt corrosion by employing copper (II), benzotriazole and the like to form a corrosion preventing film on cobalt. Although this method is capable of removing the dry etch residues, it is incapable of sufficiently suppressing the damage on cobalt (see Comparative Example 11 described later).
Patent Document 8 proposes a wiring formation method that uses a cleaning liquid containing a fluorine compound, a metal corrosion preventing agent, a passivation agent and water. This cleaning liquid, however, is incapable of sufficiently removing the dry etch residues, and thus cannot be used for the intended purpose (see Comparative Example 12 described later).